A color display unit (such as a color liquid crystal display unit) provided with a color display section (such as a liquid crystal color display section) performs display at brightness (such as lightness and transmittance of light) corresponding to the gradation of a signal provided to the color display section. Characteristics proper to the color display section arises between the gradation (gradation value) in the provided signal and the displayed brightness. Thus, in such a display unit in order that display should be performed in desired display characteristics (generally referred to as the γ characteristics) for the signal inputted to the display unit, the inputted signal is converted on the basis of a predetermined function. And after that, the signal is provided to the color display section.
As the means for performing this conversion, the color display unit comprises, in the inside, a conversion table (referred to a look-up table) for converting a display input gradation (a signal inputted to the display unit) into a display output gradation (a signal outputted after the conversion of the display input signal for the purpose of adjustment of the proper characteristics of the color display section).
In a prior art color liquid crystal display unit, a conversion table has been provided for each of the colors of R(red), G(green), and B (blue). Then, the γ characteristics has been adjusted using a single color screen for each color of RGB, so that each conversion table has been set up for each color of RGB (see, for example, Patent Document 1). Nevertheless, in a color display unit (a color liquid crystal display unit), additive color mixing does not hold exactly. Thus, when white (monochrome) is displayed using the conversion tables in each of which the γ characteristics has been adjusted for each individual single color of RGB, the γ characteristics deviates from the intrinsic γ characteristics of white. Such deviation in the γ characteristics of white causes a problem, for example, that when the color liquid crystal display unit is used for monochrome display, gradation display is not accurately performed. For example, when a roentgen photography image is displayed using a color liquid crystal display unit, higher accuracy is required in the γ characteristics of white.
[Patent Document 1] Japanese Patent Application Laid-Open No. 2002-99238.